In U.S. Pat. Nos. 4,154,448 and 4,208,056, there is set forth a rotating blowout preventor, hereinafter called a RBOP, which includes a washpipe rigidly affixed to a main body, with there being a bearing housing located externally of the washpipe for rotatably supporting a rotating head assembly. The rotating head assembly includes a removable stripper rubber assembly which is received within the washpipe and is clamped at the upper end of the rotating head assembly. The stripper rubber assembly accordingly is easily removed from the interior of the RBOP by merely unfastening the clamp means and lifting the stripper rubber assembly upwardly from the washpipe.
The above patented construction isolates the bearing housing from the returned drilling fluid. However, debris flowing uphole impact against the interface formed between the stripper rubber exterior and the washpipe interior. The debris continually and progressively accumulate, and eventually, the interior of the washpipe becomes unduly erroded. As this undesirable condition progresses, the debris eventually attack the rotating mechanical seal, accelerating the wear on the seal, until eventually the RBOP must be removed from service for repair. This condition is especially pronounced when drilling with compressible fluid, such as air or gas, because the debris can rebound several times as the axially flowing drilling fluid changes direction to flow through the lateral outlet passageway.
Accordingly, in patent application Ser. No. 202,686, now U.S. Pat. No. 4,361,185; RBOP has been provided with means by which the debris are deflected from an uphole axial direction into a lateral direction so that impact against the intervening area between the stripper rubber and the interior surface of the washpipe is precluded, thereby greatly reducing wear on some critical components of the RBOP. In U.S. Pat. No. 4,361,185 the lower marginal end of the rubber stripper has an inner annular member spaced from an outer annular member. The outer annular member has an outwardly biased skirt which sealingly engages the inner peripheral wall surface of the washpipe in order to protect the interface located therebetween from ingress of debris. The uphole or downhole thrust and various other forces which are exerted upon the stripper rubber causes the outer wall surface of the outer annular member to sometime unfavorably distort into an unsatisfactory configuration which accelerates the wear rate of the coacting parts. Accordingly, the reinforcement of the rubber in selected areas to provide control over this wear rate and to reduce the rate to a satisfactory value is the subject of this invention.